Carry on being you OP.
It’s great that he’s confronted his demons (so to speak) through therapy and he should also have the emotional tools now to cope when something triggers him. Keep those lines of communication open – that is a great form of therapy in itself if he can let you know when something’s got to him and you can both talk through it.
He will also understand that there’s no way you can know what might trigger him and the strangest of things might trigger him. The minute you start feeling like you’ve got to avoid x, y and z situation/conversation in case you trigger him is when it becomes unhealthy for you both – like others have said, treading on eggshells.
I’m in a similar situation as him, in that, I have some issues which I’ve dealt with, come to terms with through therapy and am as far as I can be but the subject can crop up from time to time – people who don’t know can randomly say something that will set me off (internally) fretting and I have the coping mechanisms for that (obviously I can't erase my past but it DOES come back to haunt me).
I’m very selective about who knows because I don’t want a pity party and I don’t want people to feel they have to behave differently around me or avoid certain topics of conversation – I know it is my issue to deal with and these people are not the cause.
It becomes a very grey area whenever I date though as that can put me in a very triggering situation and I HAVE to have a conversation with the guy about it when the time is right. I get varied responses to that conversation, ranging from ghosting, standing me up, the Slow Fade, or, the worst, “A Plan Of Action”. It isn’t a problem that needs fixing, it is an issue that needs working through dynamically, in the moment, with compassion, trust, care and patience.
So I think it is wonderful that he has found someone (you) who has that kindness and patience to not write him off as hard work when he’s already done a lot of the hard work and feels safe enough with you to talk about it. Don’t try to come up with a solution all on your own (he may well resent that) – ask him if there’s anything you can do that he would find helpful. It might make no sense to you but be open to whatever he says.
In a nutshell, carry on being you; keep the lines of communication open; it’s not your job to fix him (he’s not broken).
Caveat: If he is using this past trauma to validate any bad treatment of you then ignore all of the above and walk away.